Thrombin induces increased monocyte adhesion to HUVECs. Radiolabeled THP-1 cells, PBMCs, or monocytes were deposited on untreated or 6-hour treated thrombin- (8 U/mL) or IL-1β– (50 pg/mL) activated HUVECs and allowed to adhere for 1 hour. After cell lysis, radioactivity was counted and expressed for each condition as the percentage of adhesive cells compared with 100% deposited cells (*P < .02 compared with adhesion of respective cells on unstimulated HUVECs, n = 4). (□) Medium; () thrombin; (▧) IL-1.